Real-time air monitoring with multiple sensing modes

ABSTRACT

Embodiments of a gas detector with a first gas sensor having a first gas specificity and a first response time and a second gas sensor having a second gas specificity and a second response time. The first gas specificity is different than the second gas specificity, the first response time is different than the second response time, or both the first gas specificity and the first response time are different than the second gas specificity and the second response time. A readout and analysis circuit is coupled to the first and second gas sensors to read and analyze data from the first and second gas sensors, and a control circuit is coupled to the readout and analysis circuit and to the first and second gas sensors to execute logic that operates the first gas sensor, the second gas sensor, or both the first and second gas sensors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 61/910,910, filed 2 Dec. 2013. The priorityprovisional is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosed embodiments relate generally to gas sensing and inparticular, but not exclusively, to real-time air monitoring withmultiple sensing modes.

BACKGROUND

Gas detection and analysis can be an important means for detecting thepresence and concentration of certain chemicals in the environment anddetermining the meaning of the particular combination of chemicalspresent. For example, gas analysis can be used to determine the presenceof dangerous substances incompatible with human presence, such asmethane, carbon monoxide or carbon dioxide in a mine. But existing gasdetection and analysis systems usually involve a tradeoff between speedand gas specificity, which is the ability to identify particular gasesin a sample. Fast detectors are not specific enough, andhigh-specificity detectors are not fast enough.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1A-1D are block diagrams of embodiments of a gas detector usingmultiple gas detection systems.

FIG. 2 is a block diagram of another embodiment of a gas detector.

FIG. 3 is a block diagram of another embodiment of a gas detector.

FIG. 4 is a block diagram of another embodiment of a gas detector.

FIG. 5 is a block diagram of another embodiment of a gas detector.

FIGS. 6A-6D are flowcharts of embodiments of processes for two-modeoperation of a gas detector.

FIGS. 7A-7D are flowcharts of embodiments of processes for three-modeoperation of a gas detector.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Embodiments are described of an apparatus, system and method forreal-time air monitoring with multiple sensing modes. Specific detailsare described to provide a thorough understanding of the embodiments,but one skilled in the relevant art will recognize that the describedembodiments can be practiced without one or more of the describeddetails, or with other methods, components, materials, etc. In someinstances, well-known structures, materials, or operations are not shownor described in detail but are nonetheless encompassed within the scopeof the invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a described feature, structure, or characteristiccan be included in at least one described embodiment, so thatappearances of “in one embodiment” or “in an embodiment” do notnecessarily all refer to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

Embodiments are disclosed of a method/apparatus of monitoring real-timeambient air quality by a combination of multiple gas analysis sensingmodes, including fast-response gas sensors with low specificity tosingle compound (e.g., photoionization detector (PID), thermalconductivity detector (TCD), flame ionization detector (FID),time-of-flight mass spectrometer (TOFMS)) and slow-response gasdetectors with high specificity to each compound of interest (e.g., gaschromatograph (GC)+PID, GC+TCD, GC+FID, GC+mass spectrometer (MS)). Thegas detection modes can be operated independently (one at a time orsimultaneously in parallel) or in certain sequences based on sensingcriteria.

The disclosed embodiments can be used for gas sensing in various indooror outdoor environmental setups. In a semiconductor facility, thedisclosed embodiments can be used to ensure cleanroom air quality,ensuring the air is free of contaminants and improving process yield. Ina steel manufacturing facility, the disclosed embodiments can be used tomonitor the coke oven gas by-product leakage and process optimization.In a petrochemical facility, the disclosed embodiments can be used toidentify leaking gases and locate the source of leakage, which canprovide immediate warning and emergency response actions.

FIG. 1 illustrates an embodiment of a gas detection detector 100. Gasdetection detector 100 includes a substrate 102 on which are mountedseveral components. Gas sensor A is mounted on substrate 102 with itsinlet coupled to optional sample conditioning unit 104 by fluidconnection 101A and its outlet coupled to a pump 112. Detector 100includes gas sensor B, similarly arranged as gas sensor A, and gassensor C which is similarly arranged to gas sensors A and B except thata gas chromatograph (GC) C is coupled in fluid connection 101C betweenoptional sample conditioner 104 and gas sensor C. A controller orcontrol circuit 120 is coupled to all sample conditioners 104, tosensors A-C, to pumps 112, and to gas chromatograph C. Readout andanalysis circuit 118 is coupled to sensors A-C and also to controlcircuit 120.

Substrate 102 can be any kind of substrate that provides the requiredphysical support for the elements of gas detector 100. In oneembodiment, substrate 102 can be a single-layer printed circuit board(PCB) with conductive traces on its surface, but in other embodiments itcan be a multi-layer PCB with conductive traces in the interior of thecircuit board. In other embodiments, for example an embodiment wheredevice 100 is built as a monolithic system on a single die, substrate102 can be chip or wafer made of silicon or some other semiconductor. Instill other embodiments, substrate 102 can also be a chip or wafer inwhich optical waveguides can be formed to support optical communicationbetween the components of device 100. And in still other embodiments theelements need not be formed on a common substrate at all.

Gas detector 100 includes first, second, and third gas sensors: firstgas sensor A is a Mode A gas sensor, second gas sensor B is a Mode B gassensor, and third gas sensor C is a Mode C gas sensor. As used herein,the terms “gas sensor,” “gas detector,” or “gas detection system” can beused to refer to a gas sensor on its own or to a gas sensor incombination with other elements—such as a gas chromatograph, forinstance—or as a separate gas detection system such as gas detectionsystems A-C shown in FIGS. 1A-1D. In FIG. 1B, for example, sensor C iscoupled to gas chromatograph C, but is designated separately;nonetheless, the combination of sensor C with gas chromatograph C, aswell as other components present, can together be referred to as gasdetection system C.

Mode A sensors are real-time universal gas sensors with little or nospecificity to a single compound or to compounds with same or similarchemical property. Possible mode A sensors include, for example,photoionization detector (PID) sensors, thermal conductivity detector(TCD) sensors, and flame ionization detector (FID) sensors, but are notlimited to these. Embodiments of mode A gas sensors can detect the totalconcentration of gases in the environment (organic or non-organic) withreal-time response (less than 1 minute in one embodiment, but notlimited to this time period), but mode A detectors lack specificity todetect certain group of compounds or individual compounds separately.

Mode B sensors are fast-response gas sensors with little or nospecificity to a single compound, but with partial specificity so thatit can differentiate compounds with the same or similar chemicalproperties from other compounds with different chemical properties. Indifferent embodiments the Mode B sensors can be, for example,electrochemical sensors, metal oxide sensors, IR sensors, and e-nosesensors, but embodiments are not limited to these. Mode B sensors candetect the total concentration of certain group of gases in theenvironment (organic or non-organic) with fast response time (from 1 to10 minutes in one embodiment, but not limited to such a time period),but the Mode B detectors lack the specificity to detect individualcompounds separately.

Mode C sensors are slow-response gas sensors with high specificity tosingle compounds that require longer analysis time. In differentembodiments the Mode C sensors can be, for example, gas chromatographplus flame ionization (GC+FID), gas chromatograph plus mass spectrometer(GC+MS), gas chromatograph plus thermal conductivity detector (GC+TCD),and ion separation+MS, but are not limited to these. Embodiments of modeC detector can detect and analyze each individual compound of interestbut requires a relatively longer detection time (from 10 minutes to 120minutes in one embodiment, but not limited to this time period).

Pumps 112 are coupled to the fluid outlets of detectors A, B, and C sothat the pumps draw the gas sample into and through detectors A, B, andC and return the sample to the atmosphere. Pumps 112 can be any kind ofpump that meets the size and form factor requirements of detector 100,provides the desired flow rate and flow rate control, and has adequatereliability (i.e., an adequate mean time between failures (MTBF)). Inone embodiment, pump 112 can be a MEMS or MEMS-based pump, but in otherembodiments it need not be MEMS or MEMS-based. Examples of pumps thatcan be used include small axial pumps (e.g., fans), piston pumps, andelectro-osmotic pumps.

Gas chromatograph C, as well as other chromatographs described hereinsuch as chromatographs A, B and A/B, includes a separation column thatprovides a fluid path from an inlet of the chromatograph to an outlet,and some or all of the walls of the column are coated with a stationaryphase coating that can interact with the chemicals being separated bythe chromatograph. How thoroughly and how fast chemicals are separatedfrom the gas sample depend on the stationary phase coating, the overallpath length of the separation column, and the temperature. For a givenstationary phase coating, the longer the separation column the betterthe chemical spectrum separation, but a long column also extends theseparation time. For a given application, the required path length isusually determined by a tradeoff among the coating, the column length,and the temperature.

In one embodiment gas chromatographs used in detector 100 can be MEMS ormicro-scale chromatographs, but in other embodiments they need not bemicro-scale. In still other embodiments, any gas chromatograph used indetector 100 need not have only one separation column, but can be acascaded chromatograph with multiple separation columns arranged inseries, parallel, or a combination of series and parallel. Moreover, gaschromatograph C can include additional components such as heaters andcoolers to heat and/or cool the separation columns (e.g., athermoelectric cooler such as a Peltier device), temperature sensors,etc.

Controller 120 is communicatively coupled to the individual elementswithin detector 100 such that it can send control signals and/or receivefeedback signals from the individual elements. In one embodiment,controller 120 can be an application-specific integrated circuit (ASIC)designed specifically for the task, for example a CMOS controllerincluding processing, volatile and/or non-volatile storage, memory andcommunication circuits, as well as associated logic to control thevarious circuits and communicate externally to the elements of detector100. In other embodiments, controller 120 can instead be ageneral-purpose microprocessor in which the control functions areimplemented in software. In the illustrated embodiment controller 120 iselectrically coupled to the individual elements within detector 100 byconductive traces on the surface or in the interior of substrate 102,but in other embodiments controller 120 can be coupled to the elementsby other means, such as optical.

Readout and analysis circuit 118 is coupled to the outputs of gassensors A-C so that it can receive data signals from gas sensors A-C andprocess and analyze these data signals. In the illustrated embodiment,readout and analysis circuit 118 is electrically coupled to gas sensorsA-C by conductive traces positioned on the surface or in the interior ofsubstrate 102, but in other embodiments it can be coupled to sensors A-Cby other means, such as optical means. Readout and analysis circuit 118is also coupled to controller 120 and can send signals to, and receivesignals from, controller 120 so that the two elements can coordinate andoptimize operation of detector 100. Although the illustrated embodimentshows controller 120 and readout and analysis circuit 118 as physicallyseparate units, in other embodiments the controller and the readout andanalysis circuit could be combined in a single unit.

In one embodiment, readout and analysis circuit 118 can be anapplication-specific integrated circuit (ASIC) designed specifically forthe task, such as a CMOS controller including processing, volatileand/or non-volatile storage, memory and communication circuits, as wellas associated logic to control the various circuits and communicateexternally. In other embodiments, readout and analysis circuit 118 caninstead be a general-purpose microprocessor in which the controlfunctions are implemented in software. In some embodiments readout andanalysis circuit 118 can also include signal conditioning and processingelements such as amplifiers, filters, analog-to-digital converters,etc., for both pre-processing of data signals received from gas sensorsA-C and post-processing of data generated or extracted from the receiveddata by readout and analysis circuit 118.

In operation of detector 100, when any of sensors A-C is to be used,corresponding pump 112 coupled to its outlet is activated. The runningpump draws a gas sample into and through sample conditioner 104 and theninto and through sensor A via fluid connection 101. Having been drawnthrough the relevant sensor, the gas sample is then exhausted by pump112 into the atmosphere. The relevant sensor analyzes the gas sample andoutputs the results to readout and analysis circuit 118. Readout andanalysis circuit 118 can communicate the results of the gas analysis toa user, and can also communicate with controller 120 so that, dependingon the result, one or more of the other sensors can be activated by thecontroller depending on the results obtained by earlier-activatedsensors. In other embodiments, sensors A-C can be used independently,one at a time or simultaneously in parallel.

FIG. 1B illustrates another embodiment of a gas detector 125. Gasdetector 125 is similar to gas detector 100, except in gas detector 125the elements need not be formed on a substrate, but are grouped intoseparate gas detection systems A, B, and C: gas detection system A ismode A detection system including mode A sensing; gas detection system Bis mode B detection system including mode B sensing; and gas detectionsystem C is mode C detection system including mode C sensing with gaschromatograph C coupled to sensor C. Other embodiments of gas detectionsystems A, B, or C can include additional components such as sampleconditioners 104, additional, chromatographs, valves, etc. (see FIGS.3-5), and so on. Because they are separate systems, gas detectionsystems A, B, and C can be mounted in a rack and coupled to an externalcontroller 120 and/or readout and analysis circuit 118 which togethercan then control the three gas detection systems as shown in FIG. 6A etseq.

FIG. 1C illustrates another embodiment of a gas detector 150. Gasdetector 150 is similar to gas detector 125, but in gas detector 150 theseparate gas detection systems A, B, and C are stand-alone systems, eachwith its own controller and readout and analysis system that cancontrol, read out, and analyze the result obtained by each of thesystems. Other embodiments of gas detection systems A, B, or C caninclude additional components such as sample conditioners 104,additional, chromatographs, valves, etc. (see FIGS. 3-5), and so on.Because they are standalone systems, in gas detector 150 gas detectionsystems A, B, and C can be mounted in a rack In the illustratedembodiment, the controller and the readout and analysis circuit of eachof gas analysis systems A, B, and C is coupled to an external controller152, which can then monitor the results output by each of gas analysissystems A, B, and C, and coordinate their operation, for example asshown in FIG. 6A et seq.

FIG. 1D illustrates another embodiment of a gas detector 175. Gasdetector 175 is similar to gas detector 150, but in gas detector 175 theinlets of separate gas detection systems A, B, and C are coupled to asingle sample inlet by an optional gas sampling manifold system 185 withsingle or multiple sample inlets for detection in a single or multiplelocations. And, to reduce the number of pumps, the outlets of separategas detection systems A, B, and C are coupled to a single pump 112 by anoutlet manifold. Pump 112 is coupled to external controller 152 tocontrol its operation. As in gas detector 150, other embodiments of gasdetection systems A, B, or C can include additional components such assample conditioners 104, additional, chromatographs, valves, etc. (seeFIGS. 3-5), and so on. And, as in gas detector 150, because they arestandalone systems gas detection systems A, B, and C can be mounted in arack or otherwise be separately positioned. In the illustratedembodiment, the controller and the readout and analysis circuit of eachof gas analysis systems A, B, and C is coupled to an external controller152, which can then monitor the results output by each of gas analysissystems A, B, and C, and coordinate their operation, for example asshown in FIG. 6A et seq.

FIG. 2 illustrates an embodiment of a gas detector 200. In someembodiments, it can be useful to reduce the number of components, forexample the number of sample conditioners 104, by using a common sampleinlet instead of three separate sample inlets as in gas detector 100.Gas detector 200 includes a single sample inlet coupled to a sampleconditioner 104, which is optional and can be omitted entirely in otherembodiments. Sample conditioner 104 includes a filter/valve unit 106coupled to the sample inlet, a pre-concentrator 108 coupled to thefilter/valve unit, and an optional additional pre-concentrator 110coupled by valve 111 into the fluid line exiting pre-concentrator 108.All three elements—filter/valve unit 106, pre-concentrator 108, andexternal pre-concentrator 110—can be coupled to control circuit 120.And, as previously indicated, sample conditioner 104 is optional and canbe omitted in other embodiments.

In addition to a filter, filter and valve unit 106 also includes a valveso that further flow into sample conditioning assembly 104 can bestopped once sufficient fluid has passed through the device. Stoppingfurther flow through sample conditioning assembly 104 prevents dilutionof gases that will flow out of pre-concentrator 108 during lateroperation. In other embodiments, filter and valve unit 106 can alsoinclude a de-humidifier to remove water vapor from the gas sample andimprove the accuracy and sensitivity of downstream detectors. Inembodiments where the gas sample contains no particulates, for instancebecause it has been pre-filtered, the filter portion of filter and valveunit 106 can be omitted.

Pre-concentrator 108 receives fluid from filter and valve unit 106 andoutputs fluid through three-way valve 111 to multi-way valve 114. Asfluid flows through pre-concentrator 108, the pre-concentrator absorbscertain chemicals from the passing fluid, concentrating those chemicalsfor later separation and/or detection. In one embodiment of device 200pre-concentrator 108 can be a MEMS pre-concentrator, but in otherembodiments pre-concentrator 106 can be a non-MEMS chip scale device.

Sample conditioner 104 includes provisions for an externalpre-concentrator 110 (i.e., a pre-concentrator not mounted on substrate102). In the embodiment shown, three-way valve 111 is placed in thefluid connection pre-concentrator 106 and valve 114. Valve 111 allowsuse of external pre-concentrator 110 instead of, or in addition to,pre-concentrator 108. In one embodiment external pre-concentrator 110can be a breath collection bag, but in other embodiments it can besomething different. In an alternative embodiment pre-concentrator 108can be permanently removed and replaced by external pre-concentrator110; in an embodiment where external pre-concentrator 110 replacespre-concentrator 108 external pre-concentrator 110 can be coupledupstream of the filter and valve unit 106.

Sample conditioner 104 is coupled to valve 114. Valve 114 is a multi-wayvalve coupled to control circuit 120 so that it can be selectivelyactivated by the control circuit to direct the gas sample to sensors A,B, or C. Although illustrated as a single valve, in differentembodiments valve 114, as well as other valves described herein, can bea single valve or a combination of valves that can direct the gas sampleto each of sensor A-C individually, to all sensors A-C simultaneously,or to a subset the includes less than all sensors. If valve 114 isadjusted to direct the sample gas to sensor C, sample gas travelsthrough gas chromatograph (GC) C, through sensor C, through pump 112,and out to the atmosphere. If valve 114 is activated to direct thesample gas to sensors A and B, the sensor the sample gas encounters afurther multi-way valve 102 which is also coupled to control circuit 120so that it can be selectively activated to direct sample gas to sensor Aor sensor B.

FIG. 3 illustrates an embodiment of a gas detector 300. Detector 300 issimilar in most respects to gas detector 200. The primary differencebetween detectors 200 and 300 is that in detector 300 a multi-way valve114 is coupled to control circuit 120 to direct the gas sample to any ofsensors A-C, instead of using two multi-way valves as in detector 200.Although illustrated as a single valve, in different embodiments valve114, as well as other valves described herein, can be a single valve ora combination of valves that can direct the gas sample to each ofsensors A-C individually, to all sensors A-C simultaneously, or to asubset the includes less than all sensors. Also, in gas detector 300 agas chromatograph 112 is coupled in the fluid connection upstream ofvalve 114, so that all sensors A-C share a gas chromatograph—in otherwords, there is a one-to-many correspondence between gas chromatographand sensors. With this arrangement, any sensor selected by valve 114receives a gas sample with some prior separation of chemical species. Inanother embodiment of detector 300 chromatograph 112 can be omitted,which would make gas detector 300 similar to gas detector 200 but with adifferent valve arrangement for directing the gas sample to thedifferent sensors.

FIG. 4 illustrates an embodiment of a gas detector 400. Detector 400 issimilar in most respects to gas detector 300, except that gaschromatograph 112 is removed from upstream of valve 114 and instead gaschromatographs are put in every line downstream of valve 114, betweenthe valve and the individual gas sensors, so that there is a one-to-onecorrespondence between gas chromatographs and sensors. Hence, gaschromatograph A is paired with sensor A, gas chromatograph B is pairedwith sensor B, and gas chromatograph C is paired with sensor C. Withthis arrangement there is some separation of chemical species beforesensing, but the separated species or degree of separation can bedifferent for each sensor.

FIG. 5 illustrates an embodiment of a gas detector 500. Gas detector 500is similar to gas detector 200. The primary difference is that detector500 includes an additional gas chromatograph (GC A/B) positioned betweenvalves 114 and 202, so that sensors A and B share one chromatograph.Hence gas detector 500 has both one-to-one and one-to-manycorrespondences between sensors and gas chromatographs.

FIGS. 6A-6D illustrate embodiments of two-sensor operation of any of thepreviously-described embodiments of gas detectors. All the gas detectorembodiments described above include three sensors, but in any of thedescribed embodiments one of the sensors can be omitted. Alternatively,in an embodiment that includes three gas sensors only two need be used.Mode A results can produce much faster real-time detection result ontotal gas concentration for early warning on gas excursion. Mode Bresults (with a slightly longer analysis time than mode A), if obtained,can provide additional information on certain group of gases thatcontribute to the gas concentration excursion. And Mode C results (whichrequire longer analysis time than modes A or B), if obtained, canproduce more detailed individual concentration of specific gases thatmight be causing the excursions detected by mode A or mode B.

FIG. 6A illustrates an embodiment in which a mode A sensor and a mode Csensor operate independently, whether one at a time or simultaneously inparallel. The mode A sensor is a fast real-time universal gas detectorwith no specificity for the gases of interest, which outputs a real-timein total gas concentration results. The mode C sensor is a slowerhigh-specificity gas detector with analysis of each detected gas ofinterest, and outputs concentration results for specific gases. Whilethe mode A sensor and mode C sensor can operate at their own cyclingfrequencies respectively, one sensor's test result can be used totrigger and start the other sensor's operation, but a fast mode sensorcan keep cycling without waiting for the result from a slow mode sensor.For example, the mode A sensor may be first started in repeating gassensing cycles while the mode C sensor is not activated. When the mode Aresult satisfies certain criteria, the control electronics can activatethe mode C sensor to start its detection cycle. Both sensors can beoperating in parallel or in sequence until the repeating sensing cycleof either sensor is de-activated by the control electronics based oncertain criteria.

FIG. 6B illustrates an embodiment in which a mode B sensor and a mode Csensor operate independently, whether one at a time or simultaneously inparallel. The mode B sensor is a fast gas detector with specificity forcertain groups of gases, but no specificity to an individual gas. Themode B sensor outputs real-time total gas concentration results forcertain groups of gases. The mode C sensor, as before, is a slowerhigh-specificity gas detector with an analysis of each detected gas ofinterest that outputs concentration results for specific gases. Similarto FIG. 6A, while mode B sensor and mode C sensor can operate at theirown cycling frequencies respectively, one sensor's test result can beused to trigger and start the other sensor's operation, but a fast modesensor can keep cycling without waiting for the result from a slow modesensor. For example, the mode B sensor may be first started in repeatinggas sensing cycles while mode C sensor is not activated. When the mode Bresult satisfies certain criteria, the control electronics actives modeC sensor to start its detection cycle. Both sensors can be operating inparallel or in sequence until the repeating sensing cycle of eithersensor is de-activated by the control electronics based on certaincriteria.

FIGS. 6C-6D illustrate embodiments of a process for two-sensor operationof any of the previously-described embodiments of gas detectors. In theillustrated embodiments, activation or engagement of one sensor dependsupon the results obtained from another sensor but, as noted above, afast mode sensor can keep cycling without waiting for a result from aslow mode sensor. FIG. 6C illustrates an embodiment with a mode A sensorand a mode C sensor. The mode A sensor, as before, is a fast real-timeuniversal gas detector with no specificity for gases of interest thatoutputs real-time total gas concentration results. After operating themode A sensor, the process checks whether the mode A results meet thecriteria for activating or engaging the mode C sensor: if the mode Aresults don't meet the criteria for activating the mode C sensor theprocess reverts to operation of the mode A sensor, but if the mode Aresults do meet the criteria for engaging the mode C sensor, the processengages or activates the mode C sensor. As before, the mode C sensor isa slower high-specificity gas detector that analyzes each detected gasof interest and, if engaged, outputs concentration results for specificgases. After the mode C sensor completes its analysis, the processreverts to operating the mode A sensor.

FIG. 6D illustrates an embodiment with a mode B sensor and a mode Csensor. The mode B sensor, as before, is a fast gas detector withspecificity for certain groups of gases, but no specificity to anindividual gas; it outputs real-time total gas concentration results forcertain groups of gases. After operating the mode B sensor, the processchecks whether the mode B results meet the criteria for activating orengaging the mode C sensor: if the mode B results don't meet thecriteria for activating the mode C sensor the process reverts tooperation of the mode B sensor, but if the mode B results do meet thecriteria for engaging the mode C sensor, the process engages oractivates the mode C sensor. As before, the mode C sensor is a slowerhigh-specificity gas detector that analyzes each detected gas ofinterest and, if engaged, outputs concentration results for specificgases. After the mode C sensor completes its analysis, the processreverts to operating the mode B sensor.

FIGS. 7A-7D illustrate embodiments of three-sensor operation of any ofthe previously-described embodiments of gas detectors. Mode A resultscan produce much faster real-time detection result on total gasconcentration for early warning on gas excursion. Mode B results (with aslightly longer analysis time than mode A), if obtained, can provideadditional information on certain group of gases that contribute to thegas concentration excursion. And Mode C results (which require longeranalysis time than modes A or B), if obtained, can produce more detailedindividual concentration of specific gases that might be causing theexcursions detected by mode A or mode B.

FIG. 7A illustrates an embodiment of three-sensor operation of any ofthe previously-described embodiments of gas detectors. In theillustrated embodiment a mode A sensor, a mode B sensor, and a mode Csensor operate independently, one at a time or simultaneously inparallel. The mode A sensor is a fast real-time universal gas detectorwith no specificity for gases of interest, which outputs a real-timetotal gas concentration results. The mode B sensor is a fast gasdetector with specificity for certain groups of gases, but nospecificity to an individual gas; it outputs real-time total gasconcentration results for certain groups of gases. The mode C sensor isa slower high-specificity gas detector with an analysis of each detectedgas of interest, and outputs concentration results for specific gases.Similar to FIG. 6A and FIG. 6B, while mode A, mode B sensor and mode Csensor can operate at their own cycling frequencies respectively, onesensor's test result can be used to trigger and start another sensor'soperation, but a fast mode sensor can keep repeating its sensing cyclewithout waiting for the result from a slow mode sensor. Three sensorscan be operating in parallel or in sequence until the repeating sensingcycle of any sensor is de-activated by the control electronics based oncertain criteria.

FIGS. 7B-7D illustrate embodiments of three-sensor operation of any ofthe previously-described embodiments of gas detectors. In theillustrated embodiments, activation or engagement of one gas sensordepends upon the results obtained from another gas sensor but, as notedabove, a fast mode sensor can keep repeating its sensing cycle withoutwaiting for a result from a slow mode sensor. FIG. 7B illustrates anembodiment with mode A, mode B, and mode C sensors as in FIG. 7A. But inthis embodiment, after operation of the mode A sensor the process checkswhether the mode A results meet the criteria for activating or engagingthe mode B sensor: if they don't the process reverts to operating themode A sensor, but if they do the process activates or engages the modeB sensor. If the mode B sensor is activated, after operation of the modeB sensor the process checks whether the mode B results meet the criteriafor activating or engaging the mode C sensor: if they don't the processreverts to operating the mode B sensor, but if they do the processactivates or engages the mode C sensor, outputs the mode C results, andreverts to operating the mode B sensor.

FIG. 7C illustrates an embodiment with mode A, mode B, and mode Csensors as in FIG. 7A. In this embodiment, after operation of the mode Asensor the process checks whether the mode A results meet the criteriafor activating or engaging the mode B sensor: if they don't the processreverts to operating the mode A sensor, but if they do the processactivates or engages the mode B sensor. If the mode B sensor isactivated, after operation of the mode B sensor the process checkswhether the mode B results meet the criteria for activating or engagingthe mode C sensor: if they don't the process reverts to operating themode A sensor, but if they do the process activates or engages the modeC sensor, outputs the mode C results, and reverts to operating the modeA sensor.

FIG. 7D illustrates an embodiment with mode A, mode B, and mode Csensors as in FIG. 7A. In this embodiment, after operation of the mode Asensor the process checks whether the mode A results meet the criteriafor activating or engaging one or both of the mode B sensor and the modeC sensor. If the criteria for activating the mode B sensor are met, theprocess activates the mode B sensor and outputs the mode B results. Andif the criteria for activating the mode C sensor are met the processactivates the mode C sensor, outputs the mode C results, and reverts tooperating the mode A sensor.

The above description of illustrated embodiments of the invention,including what is described in the abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. These modifications can bemade to the invention in light of the above detailed description.

The terms used in the following claims should not be construed to limitthe invention to the specific embodiments disclosed in the specificationand the claims. Rather, the scope of the invention is to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

1. A gas detector comprising: a first gas sensor having a fluid inletfor receiving a gas sample and a fluid outlet for exhausting the gassample, the first sensor having a first gas specificity and a firstresponse time; a second gas sensor having a fluid inlet for receivingthe gas sample and a fluid outlet for exhausting the gas sample, thesecond sensor having a second gas specificity and a second responsetime, wherein the first gas specificity is different than the second gasspecificity, the first response time is different than the secondresponse time, or both the first gas specificity and the first responsetime are different than the second gas specificity and the secondresponse time; a readout and analysis circuit coupled to the first andsecond gas sensors to read and analyze data from the first and secondgas sensors; and a control circuit coupled to the readout and analysiscircuit and to the first and second gas sensors, wherein the controlcircuit can execute logic that operates the first gas sensor, the secondgas sensor, or both the first and second gas sensors.
 2. The gasdetector of claim 1 wherein the first gas sensor is a fast-responselow-specificity sensor and the second gas sensor is a fast-responsepartial-specificity sensor.
 3. The gas detector of claim 1 wherein thefirst gas sensor is a fast-response partial-specificity sensor and thesecond gas sensor is a slow-response high-specificity sensor.
 4. The gasdetector of claim 1 wherein the control circuit operates the first gassensor independently of the second gas sensor.
 5. The gas detector ofclaim 1 wherein the control circuit operates the second gas sensor ifthe result obtained from the first gas sensor meets specified criteriafor activating the second gas sensor.
 6. The gas detector of claim 1,further comprising a third gas sensor having a fluid inlet for receivingthe gas sample and a fluid outlet for exhausting the gas sample, thethird sensor having a third gas specificity and a third response timeand being coupled to the control circuit.
 7. The gas detector of claim 6wherein: the first gas sensor is a fast-response low-specificity sensor,the second gas sensor is a fast-response partial-specificity sensor, andthe third gas sensor is a slow-response high-specificity sensor.
 8. Thegas detector of claim 6 wherein the control circuit operates the first,second, and third gas sensors independently.
 9. The gas detector ofclaim 8 wherein the detector is coupled to a gas sampling manifold withsingle or multiple inlets for sampling from multiple locations.
 10. Thegas detector of claim 6 wherein the control circuit operates the secondgas sensor if the result obtained from the first gas sensor meetsspecified criteria for activating the second gas sensor.
 11. The gasdetector of claim 10 wherein the control circuit returns to operation ofthe first gas sensor when the second gas sensor has completed itssensing.
 12. The gas detector of claim 10 wherein the control circuitoperates the third gas sensor if the second gas sensor was operated andif the result obtained from the second gas sensor meets specifiedcriteria for activating the third gas sensor.
 13. The gas detector ofclaim 12 wherein the control circuit returns to operation of the firstgas sensor or the second gas sensor when the third gas sensor hascompleted its sensing.
 14. The gas detector of claim 6 wherein thecontrol circuit can select the second gas sensor or the third gassensor, depending on whether the result obtained from the first gassensor meets specified criteria for operating the second gas sensor ormeets specified criteria for activating the third gas sensor.
 15. Thegas detector of claim 14 wherein the control circuit returns tooperation of the first gas sensor when the second gas sensor hascompleted its sensing or returns to operation of the second gas sensorwhen the third gas sensor has completed its sensing.
 16. A gas analysisprocess comprising: receiving a gas sample at a gas detector including:a first gas sensor having a fluid inlet for receiving a gas sample and afluid outlet for exhausting the gas sample, the first sensor having afirst gas specificity and a first response time, a second gas sensorhaving a fluid inlet for receiving the gas sample and a fluid outlet forexhausting the gas sample, the second sensor having a second gasspecificity and a second response time, wherein the first gasspecificity is different than the second gas specificity, the firstresponse time is different than the second response time, or both thefirst gas specificity and the first response time are different than thesecond gas specificity and the second response time, a readout andanalysis circuit coupled to the first and second gas sensors to read andanalyze data from the first and second gas sensors, and a controlcircuit coupled to the readout and analysis circuit and to the first andsecond gas sensors, wherein the control circuit can execute logic thatoperates the first gas sensor, the second gas sensor, or both the firstand second gas sensors; and analyzing the gas sample using the first gassensor, the second gas sensor, or both the first and second gas sensors.17. The process of claim 16 wherein the first gas sensor is afast-response low-specificity sensor and the second gas sensor is afast-response partial-specificity sensor.
 18. The process of claim 16wherein the first gas sensor is a fast-response partial-specificitysensor and the second gas sensor is a slow-response high-specificitysensor.
 19. The process of claim 16 wherein the control circuit operatesthe first gas sensor independently of the second gas sensor.
 20. Theprocess of claim 16 wherein the control circuit operates the second gassensor if the result obtained from the first gas sensor meets specifiedcriteria for activating the second gas sensor.
 21. The process of claim16 wherein the gas detector further comprises a third gas sensor havinga fluid inlet for receiving the gas sample and a fluid outlet forexhausting the gas sample, the third sensor having a third gasspecificity and a third response time and being coupled to the controlcircuit.
 22. The process of claim 21 wherein: the first gas sensor is afast-response low-specificity sensor, the second gas sensor is afast-response partial-specificity sensor, and the third gas sensor is aslow-response high-specificity sensor.
 23. The process of claim 21wherein the control circuit operates the first, second, and third gassensors independently.
 24. The process of claim 23 wherein the detectoris coupled to a gas sampling manifold with single or multiple inlets forsampling from multiple locations.
 25. The process of claim 21 whereinthe control circuit operates the second gas sensor if the resultobtained from the first gas sensor meets specified criteria foractivating the second gas sensor.
 26. The process of claim 25 whereinthe control circuit returns to operation of the first gas sensor whenthe second gas sensor has completed its sensing.
 27. The process ofclaim 21 wherein the control circuit operates the third gas sensor ifthe second gas sensor was operated and if the result obtained from thesecond gas sensor meets specified criteria for activating the third gassensor.
 28. The process of claim 27 wherein the control circuit returnsto operation of the first gas sensor or the second gas sensor when thethird gas sensor has completed its sensing.
 29. The process of claim 21wherein the control circuit can select the second gas sensor or thethird gas sensor, depending on whether the result obtained from thefirst gas sensor meets specified criteria for operating the second gassensor or meets specified criteria for activating the third gas sensor.30. The process of claim 29 wherein the control circuit returns tooperation of the first gas sensor when the second gas sensor hascompleted its sensing or returns to operation of the second gas sensorwhen the third gas sensor has completed its sensing.